1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and is useful for reducing acoustic noise in operation.
A display device utilizing a plasma display panel is becoming commonplace as a large screen television set. As such a display device is used widely at home, it has been requested to reduce a slight noise in operation.
2. Description of the Prior Art
A surface discharge type PDP for a color display includes a partition for preventing discharge interference between neighboring cells. There are arrangement patterns of the partition including a stripe pattern that divides a display area into columns of a matrix display and a mesh pattern that divides a display area into cells. When the stripe pattern is adopted, a plurality of partitions having a band-like shape in a plan view is arranged in the display area. When the mesh pattern is adopted, one partition (a so-called box rib) that defines each cell individually in a plan view is arranged in the display area. The partition has the height of 150-200 microns and defines a gap size between the substrates in the display area.
In general, a partition is made of a low melting point glass which is burned, and is formed in the following process. (A) Low melting point glass paste is applied to a glass substrate at a uniform thickness and is dried. (B) On the dried paste layer, a mask of a pattern corresponding to the partition is formed by a photolithography process. (C) Portions of the paste layer that are not masked are removed by a sand blast method in which a cutting material is blown. (D) After removing the mask, the patterned paste layer is burned.
In the process of forming a partition, some variation of height of the partition is inevitable. Especially, when the paste layer is patterned by the sand blast method and is burned as explained above, the sand blast causes a side cut, i.e., cutting under the mask in the sand blast process, so that the edge portion of the partition may be higher than other portions in a plan view in the subsequent burning process. More specifically, when a design value of the height of the partition is 140 microns, the edge portion becomes higher than other portions by approximately 30 microns. This phenomenon is called a “raise”, and the reason of the “raise” is considered to be uneven of thermal contraction stress. The “raise” phenomenon causes incomplete contact between the substrates in a PDP manufacturing process in which one substrate having a partition is placed on the other substrate. In the major portion of the partition forming area, the upper surface of the partition contacts intimately the surface of the opposed substrate. However, at the vicinity of the “raised” position of the partition forming area, only the raised edge portion of the partition contacts the surface of the opposed substrate. As a result, the substrate is curved microscopically, and a void space is generated between the upper surface of the partition and the surface of the opposed substrate. In this state of the PDP, the substrate is vibrated locally by periodical electrostatic attraction due to an application of a high frequency drive voltage for a display. Thus, minute acoustic noise is generated. This noise drops a quality of the display operation.